It is conventionally proposed to use films made of an aromatic polyamide and/or aromatic polyimide as base films for magnetic recording media, flexible printed boards, heat sensitive transfer films, etc. since they are excellent in mechanical properties and heat resistance. The base films used in these applications are required to have a flat surface free from curling and wrinkles since the yield in processing and the functions as products are adversely affected.
It is proposed to use them as base films for magnetic recording media such as video tapes and data memory tapes which are densified especially in recent years. In these applications, the films are exposed to high temperatures when the magnetic layer is dried after coating or vapor-deposited, and they are curled or wrinkled to be poor in flatness. So, the tapes produced from them are wound in awkward styles or touch the head imperfectly, not allowing sufficient electromagnetic conversion characteristics to be obtained disadvantageously.